Speed, acceleration, and pressure controls for servomotor systems



Apnl 7, 1953 w. D. MCCOURTY E'I'AL v SPEED, ACCELERATION, AND PRESSURE CONTROLS FOR SERVOMOTOR SYSTEMS l3 Sheets-Sheet 1 Filed June 27. 1950 w. D. MGCOURTY HAL 2,633,830 SPEED, ACCELERATION, AND PRESSURE CONTROLS FOR SERVOMOTOR SYSTEMS April 7, 1953 Filed June 27. 1950 15 Sheets-Sheet 2 w. D. M COURTY EI'AL. v2,633,830 SPEED, ACCELERATION, AND PRESSURE CONTROLS FOR SERVOMOTOR SYSTEMS April 7, 1953 13 Sheets-Sheet 5 Filed June 27, 1950 %&

Apnl 7, 1953 w. D. M COURTY EI'AL 2,633,830

SPEED, ACCELERATION; AND PRESSURE CONTROLS FOR SERVOMOTOR SYSTEMS Filed June 27, 1950 15 Sheets-Sheet 4 Apnl 7, 1953 w. D. MGCOURTY ETAL 2,533,830

SPEED, ACCELERATION, AND PRESSURE CONTROLS FOR SERVOMOTOR SYSTEMS Filed June 27, 1950 13 Sheets-Sheet s v m m m 4 M .9; 1 M/ 7 m u! 1 m H m m. m 2 1 a M m m H/ w. 1\| .l' Y 5 0 l 1 H 4 v.1 a w a 1 1 I w LEE. -M, in; 1 E m m l 9. 7 M 5 April 7, 1953 Filed June 27. 1950 W. D. M COURTY EI'AL SPEED, ACCELERATION, AND PRESSURE CONTROLS FOR SERVOMOTOR SYSTEMS 13 Sheets-Sheet 7 April 7, 1953 w. D. MCCOURTY EI'AL 2,533,830

SPEED, ACCELERATION, AND PRESSURE CONTROLS FOR SERVOMOTOR SYSTEMS l5 Sheets-Sheet 8 Filed June 27, 1950 Fly. 12

Apnl 7, 1953 w. D. M COURTY ETAL 2,633,830

SPEED CELERATION PRESSURE CONTR FOR SERVOMO SYSTEMS Filed June 27, 1950 13 Sheets-Sheet 9 April 7, 1953 w. D. M COURTY EI'AL 2,633,330

SPEED, ACCELERATION, AND PRESSURE CONTROLS FOR SERVOMOTOR SYSTEMS l3 Sheets-Sheet 10 Filed June 27, 1950 V. A Elli/AS5 II n H l H Iiimmi amwsk A ril 7, 1953 w. D. M couR'rY ETAL 2,633,830

SPEED, ACCELERATION, AND PRESSURE CONTROLS FOR SERVOMOTOR SYSTEMS Filed June 27, 1950 13 Sheets-Sheet ll 2 a. a 0 ,i// 9 a m m h mwwlw fl: mm r 1 3 m M 0 6, w u 1 M .h. u m 2 u u H Y ma i u m w. A R

lug "1 M W. D. M COURTY EI'AL SPEED, ACCELERATION, AND PRESSURE CONTROLS FOR SERVOMOTOR SYSTEMS 0 \i, I I a m Z m x 5 0 2 9 w "0% w I e u 01 1 7 m W J 3mm w m =5. 1 m

Apri! 7, 1953 w. o. MOCOURTY EIAL 2,633,830

SPEED, ACCELERATION, AND PRESSURE CONTROLS FOR SERVOMOTOR SYSTEMS Filed June 27, 1950 l3 Sheets-Sheet 15 Patented Apr. 7, 1 953 UNITED STATES PATENT OFFICE SPEED, ACCELERATION, AND PRESSURE CONTROLS FOR SERVOMOTOR SYSTEMS William D. McCourty, Goldthorn Park, Wolverhampton, and Stanley R. Tyler, Willenhall, England, assignors to H. M. Hobson Limited, London, England, a British company Application June 27, 1950, Serial No. 170,604 In Great Britain June 27, 1949 s 22 Claims. (Cl. 12143) 1 Variable-speed hydraulic governors for internal combustion engines are known, comprising a diaphragm exposed to the hydraulic pressure developed by the governor and to an opposing spring pressure, which can be varied by movement of a speed-selecting member, a servomotor, comprising a servo piston movable in a cylinder and serving, when so moved, to vary the engine speed (e. g. by adjusting the flow of fuel thereto) and a control valve coupled to the diaphragm and serving, when displaced, as the result of selection of a new engine speed by variation of the load on the spring, to effect movement of the piston in its cylinder to an appropriate new position.

A governor of this kind has, moreover, the disadvantage that, due to the lag in response of the engine to movement of the servo piston, the, latter is liable to overshoot the position corresponding to the newly selected speed, with the result that the engine speed will be temporarily raised to a value beyond that selected and then changed by the controlling action of the governor to a value short of that selected. The engine speed will accordingly only reach the selected value after one or more oscillations about that value.

It is the object of this invention to provide a governor such that the tendency to overshoot the selected speed is reduced.

The invention provides, in combination with a variable speed governor body, a speed-changing device for varying the speed of the governed body, a control member movable in opposite directions from a neutral position to cause sympathetic movement of the speed-changing device, a speed-selecting member for applying to the control member a load which varies in accordance with the position of the speed-selecting member and a governor for applying to the control member a force actingin opposition to the load applied by the speed-selecting member, characterised in that the force exerted by the governor comprises a component, varying with theaccelerationoi the governed body and in creasing as the acceleration increases, and another component determined by the speed of the governed body and increasing with increase in the speed.

When, therefore, a new speed is selected the governor at once applies, in response to the acceleration of the governed body, a component of restoring force to the control member, so

overshoot and rendering the governor more stable.

The invention includes a hydraulic governor, comprising a shaft adapted to be driven by a body to be governed, a vane fixed to the shaft, a flywheel free on the shaft and having therein a liquid-filled cavity accommodating the vane, the vane being normally maintained central in the cavity, a pressure inletwhich is arranged to open, on acceleration'of the shaft, to admit pressure to the portion of the cavity in advance of thevane, a pressure-sensitive device exposed to liquid pressure in the cavity so as to be subjected to a component of hydraulic pressure which increases with the speed of the shaft and to a further component oi hydraulic pressure which increases with the acceleration of theshaft, a spring for normally maintaining said pressure sensitive devicein neutral position against the action of the hydraulic pressure, means, respon sive to movement of the pressure sensitive device from neutral position,- for efiecting sympathetic change in the speed of the governed body, and

' a manually operable speed-selecting member for reducing the t n e y o th governed body t varying the load applied by the spring to the pressure sensitive device.

, e invention includes an alternative form of hydraulic governor, which comprises a cen- .trifugal impeller arranged to be driven by the governed body, a casing mounted to rotate with the impeller, a Weight freely rotatable within the casing, a diaphragm supported by the casing andenclosing behind it a cavity in the casing, an inlet for the flow of pressure liquid to said cavity, an outlet'in the casing for allowing liquid to flow from the cavity to the interior of the casing and thence to exhaust, a valve operable on relative movement of 'the weight and casing to decrease the .efiective area of the outlet during periods of. acceleration and to increase it during periods of deceleration, a spring between the weightandjcasing for establishing a datum hydraulic pressure'difference across the diaphragm, and mechanism responsive jointly to the inipeller tip pressure and to the pressure in the cavity for adjusting-the speed of the engine so as to counteract changes in said pressures.

3, inertia wheel type of governor, Fig. 2 being a section on the line IIII in Fig. 1,

Fig. 3 is a view, similar to Fig. l, of a modified form of inertia wheel governor,

Fig. 4 is a diagram showing one specific application of a governor of the kind shown in Fig. 1, namely to the control of the constant speed unit of an airscrew.

Fig. 5 is a diagram showing the application of a governor of the kind shown in Fig. 1 to the.

control of the flow of fuel to a gas turbine engme,

Fig. 6 is a diagram showing a similar application of the governor according to Fig. 1, with the provision of acceleration limiting stops,

Fig. 7 is a diagram showing a free-piston override for the governor,

Fig. 8 is a graph showing the performance or a governor of the kind shown in Figs. l-.7,

Fig. 9 is a diagram showing an alternative'type of hydraulic governor, embodying a centrifugal impeller and associated fly weight, applied to the control of the fuel flow to a gas turbine engine installation for aircraft,

Figs. 10 and 11 are graphs indicating certain characteristics of this type of governor, when fitted with the override device shown in Fig. 12,

Fig. 12 is a diagram showing the installation of Fig. 9 but with the addition of an accelerating limiting override device,

Fig. 13 is a vertical section through another form of override device,

Fig. 14 is a section on the line XIV- XIV in i 13. V

Fig. 15 is an end elevation of a practical form of the governor shown in Fig. 9,

Figs, 16 and 17 respectively are sections on the lines XVIXVI and XVII'XVII in Fig. '15,

Figs. 18-20 arerespectivelysections on the lines XVIII-XVIII, XIX-XIX and XX--XX in Fig. 16,

Fig. 21 is a view, looking from the left-hand side of Fig. 15 and with the side cover plate removed, and

Fig. 22 is a section on the line XXII-XXII in Fig. 16.

Like reference numerals indicate like parts throughout the figures.

The basic principle of the inertia wheel type of governor shown in Figs. 1-8 will be first explained with reference'to Figs. 1 and 2.

On a shaft 22, driven by an engine or other body to be governed, is fixed a vane 23, which projects from both sides of the shaft. The two limbs of the vane 23 are accommodated in cavities .24 in aflywheel25 which is rotatably mounted on the shaft 22. The cavities 24 are filled with liquid and the vane is normally balanced against the liquid pressure acting in the high pressure sides 26 of the cavities 24 by springs 21. The high pressure sides 26' of the two cavities are connected by a passage 28 and the low pressure sides 29 of the two cavities are connected by a passage 30.

Liquid under pressure is admitted through a passage 3| in the 22 to an inlet port 3-! in a boss -25 on the .iiywheel. When-the vane 23 and flywheel 25 are rmming at the same speed, the port 3| is closed by a projection 32 on the boss of the vane. If the engine tends to accelerate, the vane 23 will overrun the flywheel 25 and the projection 32 will move from sealing position and allow liquid to flow, from the inlet passage 3|, through a passage '33 to the high pressure sides 26 of the cavities, thus tending to accelerate the flywheel.

Such a governor will, when the engine accelerates, develop components of hydraulic pressure which are responsive to speed and to acceleration. These components of hydraulic pressure may be applied, as shown in Fig. l, to a single diaphragm 34, linked as later described to the control valve of a hydraulic servomotor for controlling the speed of the engine, or they may be separately applied, for the purpose of achieving the same result, to separate diaphragms 35, 36 as shown in Fig. 3.

The speed and acceleration responsive components of hydraulic pressure may be taken from the governor in various ways by making the following alternative connections between the diaphragm or diaphragms and the cavities in the flywheel:

(1)Acceleration component only: This is ob tained, as shown in the case of the diaphragm 36' in Fig. 3, by connecting the pressure side of the diaphragm to the root of the pressure side of the vane 23, as indicated by the pasasge 3i communieating with the passage 28, and the exhaust side of the diaphragm'to the root of the exhaust side or the vane 23, as indicated by the passage 38,- communicating via a passage 3|? with the pas sage 3B. The pressure difierence across the root of the vane will then alone be effective on the diaphragm 36, and this varies with acceleration and is independentof speed.

(2) Speed component only: This may be obtained by connecting the pressure side of the diaphragm to the tip of the pressure or exhaust side of the vane and the exhaust side of the diaphragm to the root of the pressure or exhaust side of the vane. The pressure difference between the two ends of the pressure or exhaust side of the vane, which is a function of speed only and not of acceleration, will then be effective on the diaphragm.

(3) Speed and acceleration together: This is obtained as indicated in Fig. 1, by connecting the pressure side of the diaphragm 34 to the tip of the pressure side of the vane, as indicated by the passage 39 and the pressure balance slots 3%, and the exhaust side of the diaphragm to the root of the exhaust side of the vane, as indicated by the passage 38. The pressure difference across the diaphragm 34 will then depend both on the pressure difference between the root and tip of the vane 23, which varies with speed, and the pressure diiference across the root of the vane, which varies with acceleration.

When the third method of connection is adopted, a single diaphragm may be used, as shown in Fig. l, but when the speed and acceleration components are separately picked up a pair of diaphragms will be used, one responsive to each component and both linked to a single control valve.

Where two diaphragms are so employed, the speed component need not be picked up from the flywheel but can, as an alternative, and as shown in Fig. '3, be picked up by establishing connections to, 4| to opposite sides of the speed responsive diaphragm 35 from the tip and eye of acen-trifugal impeller 42 mounted on the shaft 22 carrying the vane, or on a shaft geared to that shaft. The diaphragms 35, 36 are linked by a beam 43, pivoted at 44 to a lever 45 mounted on a fixed pivot 45 and carrying the control valve 41 of a hydraulic servomotor, which operates to control the speed of the governed body as later described The acceleration sensitive diaphragm 36 is loaded by a spring '48 and the speed sensitive diaphragm 35 is loaded by a spring 49, the load of which is adjustable by means of a cam 50.

As an alternative to providing the vane 23 with springs 21, these may be omitted and the port 32 made double acting so that, on deceleration, the vane 23 will, by lagging behind the flywheel 25, allow pressure to be admitted to the low pressure sides 29 of the cavities in the flywheel, Fig. 6.

The flywheel-type hydraulic governor shown in Figs. 1-3 is particularly suitable for use with internal combustion engines, especially gas turbine engines, and some applications of this use will now be described.

The first application, shown in Fig. 4, is to the case of an internal combustion engine driving a constant speed airscrew. The pitch of the blades is controlled by a hydraulic. servomotor, comprising a piston and cylinder 52 controlled by a relay valve 53 which is movable, from the neutral position shown, to effect, through lines 54, 55, alternative connections between opposite ends of the cylinder 52 and a pressure line 56 and return line 51. The relay valve 53 is connected to a diaphragm 58 disposed in a chamber 59 having a passage 60 affording a. restricted flow for liquid from one side of the diaphragm 58 to the other. A spring 6| acts on the low pressure side of the diaphragm 58 and liquid flows from this side of the diaphragm through the interior of the relay valve 53 and out to the exhaust side of the governor diaphragm 34, the flow out of the relay valve being controlled by a control valve 41 attached to the governor diaphragm 34. This valve 4! comprises an abutment 62, attached to the governor diaphragm, and having a flat surface opposite the end of the relay valve 53, and a half ball valve 63 loaded by a spring 64. The governor diaphragm 34 is loaded by a spring 49 and the pressure difference across it, developed by connecting its high pressure side through line 39 to the tip of the pressure side of the vane 23 and its exhaust side through line 38 to the root of the exhaust side of the vane, normally balances the pressure of the spring 49.

If the engine speed deviates from the selected value, the governor diaphragm 34 will move to increase or reduce the area of the outlet from the relay valve 53, so causing the diaphragm 58 to move the relay valve 53 and cause the servo piston 5| to adjust the blade pitch .in the direction to return the engine speed to the selected value, the movement ceasing by reason of return of the governor diaphragm 34 and relay valve 53 to their initial position.

'A speed-selecting lever 65, movable about a pivot 66, has teeth meshing with rack teeth on a sleeve 6'! constituting an abutment for the spring 49 and, when moved from its slow running position S.R.. towards its full throttle position F.T. to select a higher speed, the lever 65 compresses the spring 49 and causes the diaphragm 34 to move to the left to increase the flow from the open end of the relay valve 53. The resulting movement to the left of the relay valve 53 causesthe servo piston 5| to fall, thereby actuating pitch changing mechanism, not shown, coupled to the piston'rod 68' to change the blade pitch to a value corresponding to a higher engine speed. Immediately, however, the engine begins to accelerate the resulting movement of the vane 23 in relation to the flywheel 25 develops'a hydraulic pressure tending to'return the governor diaphragm 34 to its original position. Asthe engine speed increases more of the pressure drop across the governor diaphragm is supplied by the speed-responsive component of the diaphragh-controlling pressure differential, leaving less supplied by the acceleration-responsive component. This means that as the engine speed approaches the newly selected speed the rate of acceleration decreases until, when the desired speed is reached, the acceleration is zero and, therefore, steady running conditions are obtained.

The characteristic of an installation of this type is shown in Fig. 8. On movement of the lever 65 to accelerate the acceleration increases rapidly as indicated by the line 0A, the slope of the line being due to friction and the inertia of the system. Thereafter, the acceleration gradually decreases, as indicated by the curve AB. Meanwhile, the speed gradually increases, as indicated by the curve 0G, to the selected final value represented by BC.

When the speed-selecting lever 65 is moved in the direction to decelerate, the load on the spring 49 is reduced, the diaphragm 34 and relay valve 53 moving to the right and the servo piston 51 rising in its cylinder to reduce the engine speed.

While reference has been made to movement of the servo piston 5| in Fig. 4 actuating the I pitch-changing mechanism of a constant speed airscrew, the installation of Fig. 4 may be used to control the engine speed in other ways. Thus, for example, the servo piston 5| may be utilized to control the delivery of a variable stroke fuel pump, or to vary the amount of fuel supplied to the engine from a constant stroke fuel pump.

The control valve linked to the governor diaphragm may, as later described, control the engine speed by effecting movement of a servo pis ton, arranged to regulate the flow of fuel to the engine either by adjusting the position of a needle valve controlling the fuel flow or by adjusting the delivery of a variable delivery pump. In this case the above-described relay valve can be omitted, and the servo piston may have a restriction allowing fuel to flow through it from the high pressure end of the cylinder and thence to the exhaust side or the governor diaphragm through the control valve, the piston being loaded by a spring acting on its low pressure side. The control valve willthen, owing to the effect of the rate of the spring, assume slightly different controlling positions for each selected speed.

It has been explained above that, where use is made of the known type of governor which ap plies to the. diaphragm a restoring force which is dependent on speed only, the servo piston is liable, during period of acceleration, to travel to the end of its stroke, on movementof the control valve from controlling position, ,due to the lag in response of theengine. With the governor according to the invention, however, this tendency is prevented 'due to the acceleration-responsive component of restoring force which, even though the servo piston may initially overshoot the position correspondingto the newly-selected speed, wil1,by returning the diaphragm and control valve towards controlling position at an early stage, cause the servo piston to return to its correct position, should it have overshot' it, before the engine can attain aspeed beyond that selected.

In the case of a gas turbine, in which the speed is regulated by the amount of fuel feol' to the engine, some form bf overriding device will generally be desirable in order to prevent overfueling durin acceleration-and/or weak-mixture blow-out on deceleration.

- This overriding device may take one of a ber of forms, for example:

(a) When the control operates a variable delivery pump a stop could be incorporated in the pump so as to limit the effective stroke. The position of this stop could be arranged to vary with R. P. ML, air intake pressure, air intake temperature, turbine temperature, or other variable factors.

(b) A fuel/ air ratio control could be arranged to limit the effective stroke of the pump or spill excess fuel as necessary, this control being re sponsive to the pressure dependent upon the weight of air passing through the system.

(c) A control sensitive to jet velocity and/or jet pipe temperature, could act as the override.

Various forms of governoraccording to the invention, in which the servo piston controls the rate of flow of fuel to the engine and which incorporate an override within the governor itself will now be described.

In the arrangement of Fig. 5, fuel is pumped to a gas turbine along a pipe 69 and thence, through a pressure maintaining valve Hi, to a pipe H leading to the burners. The quantity of fuel supplied to the engine is controlled by a needle num valve '52 attached to the servo piston 51 and controlling the amount of fuel spilt back to the suction side of the pump through a passage 13, a pressurising valve 74 and a passage 15. Fuel passing the needle valve 12 passes through a pressure reducing valve and thence through a conduit 7'! to the highpressure end of the servo cylinder 52. Fuel also passes through a restricted orifice is to the low pressure end of the cylinder 52 and thence, through a pipe T9, the outlet area of which is controlled by the control valve ll, to the low pressure sides of the two diaphragms 3t, 36 and thence via a passage 80, to the passage 15. The servo piston 5 I is balanced against the pressure difference across it by a spring 8!.

As will readily be understood, movement of the lever 65 to increase the load applied by the spring 49 to the diaphragm 34 will open the valve 4'1, thereby causing the servo piston 5| to move to the left, closing the needle valve 12 and increasing the flow of fuel to the engine. Movement of the lever 65 in the opposite direction will close the valve 41, and cause the servo piston 5| to move to the right and decrease the fuel flow to the engine.

In the arrangement of Fig. 5, the diaphragm 34 is, as in the case of Fig. 1, exposed to both the speed and acceleration components of restoring force derived from the flywheel. A diaphragm 36 responsive to acceleration only, is coupled by a rod 82 to a third smaller diaphragm 83 exposed, like the diaphragm 34, to the combined pressure differential. This rod 82 is pivoted to the end of a lever 84, pivoted on an adjustable pivot 85 carried by a pivoted lever 86 which may be displaced, to vary the position of the pivot 85, by an altitude-responsive capsule, not shown. The lever 84 carries a pad 81 located at the high pressure side of the main diaphragm 34. A spring 390, the pressure of which is adjustable by a screw bears against the underside of the diaphragm 36.

This arrangement does not limit the weakening of the mixture obtainable on deceleration. When, however, the pilots lever 65 is moved in the directionto accelerate, the control valve 41 opens and the acceleration component. acting oil-the underside of the diaphragm 36, applies a direct force on the main diaphragm 34, via the pad 81, in the direction to close the control valve 41, so limiting the extent to which the servo piston 5| can enrich the mixture. With this arrangement the maximum acceleration varies with the square of the speed. The altitude-responsive capsule varies the position of the intermediate pivot of the lever 84 and therefore the amount of force in the valve-closing direction which can be exerted by the pad 81. I

In the arrangement shown in Fig. 6, as in the case of Fig. 3, the control valve 4'] is linked to tWo separate diaphragms, viz. a diaphragm 35 loaded by the adjustable spring 49 and balanced against this, through connections 40, 38, by a pressure differential determined by speed only, and a diaphragm 3B loaded by a spring 48 and balanced against the spring pressure, through connections 3?, 38 by a pressure difierential determined by the acceleration only. The first diaphragm 35 may be coupled to the flywheel 25 by the connections described above, or may receive its pressure differential, as in the case of Fig. 3, from a centrifugal impeller mounted on the vane shaft 22.

The two diaphragms 35, 36 are connected to opposite ends of the link d3 pivoted intermediately of its length at M to one end of the lever, which is pivoted centrally on a fixed pivot 45 and carries the control valve t! at its other end.

The diaphragm 35 carries, on its pressure side, a rod 88 fitted with a collar 89 movable between stops 9! carried on a pair of scissor links 39, pivoted together at 92. 'The remote ends of the links 99 are held by a spring 93 against a needle 94 carried by a third diaphragm t5, loaded by a spring 96 and subjected through the connections 33 to a pressure differential varying with speed and ambient pressure. As the speed increases, the diaphragm 95 responds by drawing the needle 94 away from the ends of the links 90, enabling these ends to close and increasing the clearance between the stops 9| constituting the other ends of the links 90.

When a higher speed is selected, the increased compression of the spring 39 acting on the diaphragm 35 moves the linkage 43, 45, to close the control valve ll, causing the servo piston 5i to move up to actuate, through its piston rod 68, a variable delivery fuel pump or a spill valve so as to increase the fuel flow to the engine. The resultant response of the diaphragm 35 to acceleration of the engine at first causes the link 43 to pivot about its pivot M without re-opening the valve 3?, until the collar 89 on the rod 88 coacts with the upper stop 5!. Thereafter. further action of the acceleration component on the diaphragm 3S actuates the lever 45 to open the valve 4?. The stops 94 act in precisely similar fashion on selection of a lower speed to limit the degree of deceleration which can be produced before the valve 41, which opens on selection of a lower speed, can be closed.

The stops 9| thusrestrict the acceleration or deceleration obtainable, permitting an initial movement of the acceleration-responsive diaphragm 35, before the valve ll isaffected, which varies with the actual engine speed.

It is believed that, for gas turbine engines, the desideratum is that the maximum acceleration should be directly proportional to the speed. This can be achieved by using a square law spring for loading the diaphragm 55 in opposition to the pressure differential acting on it, which, of course, is proportional to the square of the speed. Alternatively it may be achieved by using a constant rate spring and by suitable shaping of the needle 94 attached to the diaphragm 95. By giving another shape to this needle 94 a different desired relationship between maximum acceleration and enginespeed can be obtained.

The maximum acceleration for any given speed may need to be altered with variations in air intake pressure. This is provided for in Fig. 6 by a pressure sensitive capsule 91 operating a needle 98 which controls an orifice in a spill line 99 from the upper side of the diaphragm 95 and so, depending on the size of the restriction in the spill line 99, adjusting the position of the needle 94 and therefore of the stops 9|.

In the arrangement shown in Fig. '1, a single diaphragm 34, responsive both to speed and acceleration, is used to operate the control valve 41. The override device is constituted by a free floating piston I00 having a bleed orifice IOI and loaded by springs I02 against movement in either direction in the servo cylinder 52. With such an arrangement the servo piston and free piston I00 move together during their initial travel. When, however, the free piston I00 has moved to the limit permitted by'its springs I02 and is arrested, by one or other of a pair of stops I03, further movement of the servo piston 5I is retarded due to the restriction to flow imposed by the bleed orifice IOI in the free piston I00. The servo piston 5I in this case will be coupled to a specially shaped needle valve, not shown, the shape of which will govern the maximum possible enrichment or weakening of the mixture supplied to the engine.

An alternative form of governor will now be described, first with reference to the diagram in Fig. 9 and to the practical embodiment shown in Figs. 15-22. Reference characters other than those used in Figs. 1-7 are employed to designate the parts of the alternative form of governor described with reference to Figs. 9-22. Like reference characters, however, denote like parts throughout these figures.

Referring first to Fig. 9, fuel from a tank I0 is fed, through a normally open cut-off valve I I, to a pressure line I04 by a gear pump I05 and thence, through a pressure boost valve I06, to a line I09 leading to the burner ring of a gas turbine. Fuel from a starter boost pump may be introduced into the system for starting purposes, along a line I I0 and through a non-return valve III. Line I09 is also connected to a normally closed dump valve I08. By operation of a linkage II2, a normally open engine stopping valve I01 and the normally closed dump valve I08, can be moved, from the positions shown, to a position in which the valve I01 closes line I09 and allows fuel from the pump I05 to be returned to the suction side of the pump via a line H3, and the valve I08 connects the line I09 to a dump line I I4, so allowing any fuel remaining in the burner ring to be spilled away.

The flow of fuel to the engine is regulated by a needle valve I I5, attached to a servo piston I I6, movable in a cylinder 1. The needle valve I I5 allows part of the fuel from the line I04 to flow back to the suction side of the pump through a line II8 containing a spring loaded pressurising valve I I9. Fuel from the downstream side of the metering needle I I5 can pass, through a passage I20, to the left hand end of the servo cylinder and thence through a restricted orifice I2I in the servo piston to a line I22, the outlet from which is controlled by a control valve I23. The servo piston I I6 is balanced against the liquid pressure difference across it by a spring I24, and the pressurising valve II9 ensures that the servo system will be operated by fuel at constant pressure.

Turning now to Figs. 15-22, the governor comprises a central drive shaft I25 (Fig. 16) having thereon splines I26 by means of which it may be driven. Driven by the shaft I25 is one of the gear wheels I05 of the pump. Fuel from the inlet I21 (shown in Figs. 15-11) reaches a passage I28 (Fig. 19) and is pumped by the gear wheels I05 along a passage I29 (Figs. 17 and 18) to the needle valve II5. Fuel from the pump flows, through the pressure boost valve I06 (Fig. 18) and the valves I01, I09 to an outlet I30,

which will be connected to the burner ring. In Fig. 18 the inlet for connection to the starter boost pump is shown at I3I. On rotation of a lever I32 (Fig. 15) external to the casing of the governor, the engine stopping valve I01 and the dump valve I08 can be moved to their alternative positions described above. Normally, fuel can flow from the pressure boosting valve I06 to the outlet I30 through a central port I35 in the valve I01 as shown in Fig. 18. When the valve I01 is rotated clockwise through from the position shown in Fig. 18, liquid is passed by the pressure boosting valve I06 to a port I39 in a sleeve I34 surrounding the valve, which port is connected by a passage, I30 (see also Fig. 16), to the space I31 on the low pressure side of the pressurising valve II9. This space is connected by a passage I 31 to the inlet I21. At the same time, a port I38 (Fig. 16) in the valve I01 connects the outlet I30, via a port 330 (Fig. 18) in the sleeve I34 to the space 33I (Figs. 16 and 22) surrounding an eccentric I33 on the end of the valve I01. As shown in Fig. 22, counterclockwise rotation of the valve I01 as there seen causes the eccentric I33 to lift the dump valve I00 against a spring 332, so connecting the space 33 I, and therefore the outlet I30, to a union I39 (see also Fig. 15) leading to the dump line.

Fixed to the shaft I25 is a cylindrical casing I40, which carries on each face a set of impeller vanes I4I, which are shown in Fig. 9 as a conventional centrifugal impeller I4I. For clarity in Fig. 9 the casing I40 is drawn in the same plane as the shaft I25 carrying it.

As shown in Figs. 9, 16 and 20, a fly-weight I42 of approximately dumb-bell shape is rotatably mounted within the casing I40. The flyweight I42 is supported on pins I43 (Fig. 16) which turn in bearings in relation to the portions of the shaft I25 on opposite sides of the casing I40. The casing carries two bosses I44, I45 (Fig. 20). The casing I40 rotates anticlockwise as seen in Fig. 20 and the boss I45 has in its leading face a cavity I48- closed by a diaphragm I49 which faces the trailing edge of on limb I50 of the fly-weight. The trailing edge of the other limb I5I of the fly-weight carries a half-ball valve I52 which, when the casing I40 and fiy-weight I42 are rotating at equal speeds, is spaced slightly in advance of the other boss I44 on the casing in which is an outlet I53 for fuel.

A fuel inlet passage I54 leads to the cavity I48 behind thediaphragm I49 and a passage indicated at I55 leads to the outlet I53 controlled by the half-ball valve I52. Fuel is supplied from the downstream side of the needle valve II5, througha passage I46 (Fig. 18) to one side of an 11 acceleration responsive diaphragm I63 and thence through a pipe I41 indicated in Figs. 9, 16 and 20, to a passage I41 (Figs; 16 and 20). The passage I41 communicates with the passage I55 and also with a passage I54 leading to the passage I54. Fuel can flow through the outlet I53 into the interior of the casin I40 and thence, through holes I56 in the casing, to an annular space in the housing I 51 surrounding the casing, which space is subject to impeller tip pressure. The impeller tip pressure is applied, through a pipe I58 (Fig. 16) to a speed responsive diaphragm I62 as later described. The eye of the impeller I4I is connected to the inlet by a pas-'- sage indicated at I59 in Figs. 9 and'l'6'. Springs I60 interposed between the leading edge of each limb of the fly-weight I42 and the trailing edge of the adjoinin boss normally maintain a rod ISI carried by the fly-weight I42 in contact with the diaphragm I 49 and establish a datum hydraulic pressure difference across the diaphragm.

If the engine accelerates, the fiy-weight I42 will lag behind the casing I46 and the effective area of the outlet I53 will be reduced, thereby causing a rise in pressure in the cavity I48 which is a measure of the acceleration. If the engine decelerates, the casing Hi6 will lag behind the fly-weight I42, thereby increasing the effective area of the outlet its and producing a decrease in the pressure in the cavity I48 which is a measure of the deceleration.

The governor controls the fuel flow through the agency of two diaphragms one, -62, responsive to speed and one, I63, responsive to acceleration. These diaphragms are shown most clearly in Figs. 18 and 21. The control valve I23 is supported on a beam I64 coupling the two diaphragms.

The fuel from the right hand end of the cylinder I I1 flows through the outlet from the line I22 (Figs. 9 and 17), under control of the valve I23 and thence to the low pressure sides of the diaphragms I62, I63, the fuel returning thence to the inlet by a passage indicated at I65 in Fig. '9. The fuel from passage I46 (Fig. 9) passes through a restricted orifice I66 to the pressure sides of the diaphragm I63 and thence, through "the pipe I41 already referred to, to the inlet I54 to the cavity 148. The pressure inthe cavity I48'is thus applied to the acceleration responsive diaphragm I63.

The pipe I58 already referred tocommunicates, via'an adjustable needle valve I61 (Fig. 16) fitted with a finial nut I95, and a passage I68, with the pressure side of the speed responsive diaphragm I62, so applying a proportion of impeller tip pressure to'that diaphragm.

The acceleration responsivediaphragm I63 is balanced against the liquid pressure difference on it by a spring I6 (Fig. 18) the loading of which is adjustable by a screw I69 fitted with -a finial nut I10. In the event of acceleration of the engine, the diaphragm I63 moves, in response to the change of pressure in the cavity I48, to open the control valve I23. It-mov'es in the reverse direction in the event of deceleration.

The speed responsive diaphragm I62 is balanced against the liquid pressure diiierence across it by a spring IN, the loadingof which is adjustable by means of a lever I12 (Figs. 15 and 16). This is operable from a pilots speed control lever in the cockpit. As shown in Figs. 16 and 18 the lever I12 is fixed to a shaft I13 carrying-a toothed quadrant I14 meshing with rack teeth I15 -on a sleeve I 16 constituting an 'abutmentforlthe spring HI. Adjustable stops I11, I18 fitted with finial nuts I19, I60 coact with the quadrant I 14 to limit the movement which may be imparted to the lever I12. The diaphragm I 62 serves to open the control valve I23 in response to increase in engine speed and to close it in response to decrease in engine speed. The rate of the spring I1I is proportional to the selected speed, so that the sensitivity of the governor is substantially constant over the whole speed range. Adjustable stops I8I, I62 fitted with finial nuts I83, I84 are provided opposite each face of the speed responsive diaphragm I62, these serving to set the maximum positive and negative values of the acceleration of the engine.

The half=ball control valve I23 is supported on a housing i655 of rectangular shape and forming a seating for the valve I23. A spring I86, acting on a collar I81 on the valve, holds the valve I23 on its seating. A spring plate 333 (Fig, 1'1) riveted to the housing I85 is fixed under side plates #63 and serves to restrain the beam I6 3 against transverse and fore and aft movement. The housing I85 is rotatable on trunnions I69 (Fig. 17) carried by the beam I64 about an axis transverse to the length of the beam.

At one end, the beam I6 3 carries a thin spring plate I33 by which. it is attached to the diaphragm I62, the plate I93 being held under constant tension by a spring I9! At its other end the beam H34 carries a pin its which abuts against a projection 33s on the diaphragm I63, 'a spring I92 being interposed between the beam I64 and the diaphragm I63.

When a higher speed is selected, the speed responsive diaphragm I62 is moved, by the increased load imparted to its' spring I1I, until arrested by the adjustable stop I'BI. This, through the agency of the spring plate 'I 93, rocks the beam, antiolockwiseasiseen in Fig. 18, to close the control valve I23 and also to increase the load on the spring I6 associated with the acceleration responsive diaphragm I63. Application of acceleration pressure to the diaphragm I63 will only cause the beam 64 to move in the direction to reopen the control valve I23 when the additional load so placed on the spring in? has been overcome. The other stop- I62 serves to limit the initial movement of the speed responsive diaphragm I62 when a lower speed is selected.

By adjustment of the needle I61, the desired relationship between speed and acceleration pressures maybe maintained notwithstanding manufacturing errors in the unit, changes .in specific ravity of the fuel and changes in drive ratio between the engine and the governor unit.

The governor, shown in Fig. 9 and in Figs. iii-22, may, like thoseof the fly-wheel type previously described, in certain cases need to be fitted with an override to prevent over-fuelling on acceleration and/or 'fiame extinction on deceleration. This override may be of any of the following types:

(a) When the servomotor,:instead of operating a metering needle to spillback to the suctionside part of the delivery of a ffixed delivery pump, varies the fuel flow by adjusting a variable delivery pump, a stop could be incorporated in the pump to limit its maximum or minimum delivery. The position of this stop could-be arranged to vary automatically-withchanges in R. P. M.. air intake pressure orother variable factors.

(b) A fuel-air ratio control could be arranged to limit the maximum and minimum'delivery of the fuel pump to values dependent upon the weight of air passing through the engine at any given time.

(c) A control unit could vary the position of the stops I8i, I82 for the speed responsive diaphragm I82 in accordance with changes in R. P. M., air intake pressure or other variable factors so providing varying values for the maximum and minimum acceleration.

(d) A control unit could measure the amount of fuel passing to the engine, e. g. by measuring burner ring pressure, and limit the maximum and minimum amount supplied in accordance with changes in R. P. M., air intake pressure or other variable factors.

(e) A control unit could measure the engine acceleration and equate it to some pressure which varies with R. P. M., air intake pressure or other variable factors so providing varying values for the maximum and minimum acceleration.

metering needle H in the direction to increase the flow of fuel to the engine. Thus a spill line I94, Fig. 9, may be provided for allowing fuel to spill from the line I22 when the override valve (not shown in Fig. 9) opens. The spill line may be connected to the governor shown in Figs. 15-22 by means of an outlet I96 (Fig. 18) which is there shown plugged by a screw I91.

One specific form of override mechanism for overriding the normal action of the governor described above with reference to Figs. 9 and 15-22 is shown in Figs. 13 and 14. This is intended for torque converting devices and at such times as the freely driven member tends to overspeed, the override which is driven by the free member reduces the fuel supply to the engine,

thus overriding the speed selection of the main governor.

The override comprises a housing I98 0011-.

taining a shaft I 99 fitted with splines 200 by means of which it may be driven at some fractrolvalve 200. This. is normally maintained in position to close the outlet 205 due to the pressure of a spring 2 I2 located between the fly-weight 2| I' and the bridge piece 202. Tails 2I3, 2 on Pivoted at 201, 208 to-the fly-weight the bob-weights 209, 2| 0 bear against the flyweight 2 and urge it in the direction to com- When the unit is rotated weight 2: 'Thisunit is, therefore, "fully me-; chanical. The opening of'the control valve 206.

which occurs when the sum of the centrifugal and inertia forces reaches a value equal to the spring setting, allows fuel to flow from the inlet 203 connected to the spill line and through the valve to an outlet 3I3 connected to the suction side of the pump. This results in a rapid reduction of pressure at the low pressure end of the servo cylinder II'I (Fig. 9) and consequent movement of the piston H6 and metering needle H5 to reduce thede'li'very of the pump. When the speed and/or acceleration drop to a given value, -'the valve 206' closes again and the main governor unit resumes control'over the engine peed 7 V V Reference has been made above to the desirability of providing an-override, for preventing over-fuelling during acceleration, which will measure the engine acceleration and equate it with some pressure that' varies with R. P. M., air intake pressure or othervariable features, so providing varying values for the maximum and minimum acceleration. :Such an override is shown in Fig. 12, which is a replica of Fig. 9 but with the override added. This override includes an override valve 2M in parallel with the halfball control valve I23, which opens when the pressure developed across a diaphragm 2II by the acceleration component of the controlling pressure developed by the governor exceeds a value dependent on (a) a fixed minimum, (b)"'a value proportional to the square of the engine R; P.M. and (a) pressure in the engine nace1le.-

These. values are shown graphically in Fig. 11.

The override valve 2H!- normally closes an outlet 2I5 from the spill line, I94. The seating 2H5 for the valve 2M is attached to the diaphragm 2 I I, which is subjected on its upper face, through a line HR, to the acceleration pressure acting on the acceleration responsive diaphragm I63. A line-2l9 connects the space beneath the diaphragm 2I1 to the return line I65. 'The diaphragm '2I'I is biassed by a spring 220, the strength of which decides the minimum value of acceleration pressure at which the diaphragm 2|! will move down to open the override valve A'second' diaphragm 22l is subject, on its lower surface and through line 222, to the pressure at the tip of the impeller MI, and a spring 223 biasses the diaphragm 22l so that at low speeds, an extension 224 of the diaphragm 22I is maintained out of contact with the seating 2I6.

The characteristics of the governor override shown in Fig. 12 are illustrated in Figs. '10 and 11.

The speed of the engine, at time t, is given by the formula dn -8. KAe I where 85 is an initial speed and A and K are constants. The acceleration, at time t, is consequently override valve 2 l4 opening to restrict the acceler-i ation as indicated by the line PQ; As will be seen, the override limits the acceleration to the value 'OP, i. e., R..P.M./sec., until the speed 

